Ørsted was giving a lecture demonstration when he noticed that a compass needle placed near a wire carrying electric current suddenly deflected. When the current was turned off, the compass returned to its original orientation. This simple observation showed conclusively that moving electric charges (current) create a magnetic field around them, just like a permanent magnet.

The pattern and direction of the magnetic field generated by an electric current depend on the shape of the conductor.

1. Straight Current-Carrying Wire:
2. The magnetic field lines produced by a straight current-carrying wire form concentric circles around the wire. The field is strongest closest to the wire and weakens as you move further away.
3. The direction of these circular magnetic field lines can be determined using the Right-Hand Grip Rule (also known as the Right-Hand Rule or Ampere's Rule): If you grasp the wire with your right hand, pointing your thumb in the direction of the conventional current (positive to negative), your curled fingers will indicate the direction of the magnetic field lines.
4. Current-Carrying Loop/Coil:
5. When a straight wire is bent into a circular loop, the magnetic field lines from each segment of the wire combine and reinforce each other.
6. Inside the loop, the magnetic field lines are concentrated and generally point in the same direction, making the loop behave like a small, flat bar magnet.
7. The Right-Hand Grip Rule can also be applied here: If you curl the fingers of your right hand in the direction of the conventional current around the loop, your thumb will point in the direction of the magnetic North pole of the loop.
8. Solenoid (Electromagnet):
9. A solenoid is essentially a long coil of wire that is wound into a tightly packed helix. When an electric current flows through the wire of a solenoid, it produces a magnetic field that is remarkably similar to the field of a bar magnet.
10. The magnetic field created inside a solenoid is strong and nearly uniform (parallel lines). Outside the solenoid, the field is much weaker and spreads out.
11. The strength of the magnetic field produced by a solenoid can be significantly increased by:
    • Increasing the current (I): More current means a stronger magnetic field.
    • Increasing the number of turns (N): More loops of wire (denser winding) mean a stronger field.
    • Inserting a ferromagnetic core: Placing a material like soft iron or steel within the center of the solenoid greatly concentrates and strengthens the magnetic field. This is how a practical electromagnet is made.
12. The Right-Hand Grip Rule also applies to solenoids: Curl the fingers of your right hand in the direction of the current flowing through the coils, and your thumb will point towards the North pole of the solenoid.

An electromagnet is a type of magnet whose magnetic field is produced by an electric current. Unlike permanent magnets, electromagnets offer unique advantages:
- Controllable Magnetism: Their magnetic field can be turned ON or OFF simply by switching the current on or off.
- Variable Strength: The strength of the magnetic field can be precisely controlled by adjusting the amount of current flowing through the coils, or by changing the number of turns in the coil.
- Reversible Polarity: The North and South poles of an electromagnet can be reversed by simply reversing the direction of the current flow through the coil.

How a Simple Electromagnet is Made: A basic electromagnet can be constructed by wrapping insulated copper wire around a soft iron core (like a large iron nail or bolt) and connecting the ends of the wire to a battery or power supply. The iron core becomes magnetized when current flows, and it loses its magnetism when the current is switched off.

Widespread Applications of Electromagnets: Electromagnets are integral to countless technologies that shape our modern world:
- Electric Bells: An electromagnet pulls a hammer to strike a gong when current flows, then releases it when the circuit is broken, causing continuous ringing.
- Relays: Electrically operated switches. A small current activates an electromagnet, which then closes or opens contacts in a separate circuit, allowing a small current to control a much larger current or voltage.
- Lifting Magnets (Cranes): Used in scrap yards to lift and move heavy iron and steel objects. They can pick up large quantities of metal and then release them instantly by turning off the current.
- Magnetic Resonance Imaging (MRI) Machines: Medical devices that use powerful electromagnets to generate strong magnetic fields, which are used to create detailed images of organs and structures inside the body.
- Maglev (Magnetic Levitation) Trains: These innovative trains use powerful electromagnets to lift the train above the tracks (levitation) and propel it forward, reducing friction and allowing for very high speeds.
- Speakers and Microphones: Electromagnets play a crucial role in converting electrical signals into sound (speakers) and vice-versa (microphones).